حاصل عبارت های زیر را به دست آورید: الف) $\frac{1}{\sqrt{5}+\sqrt{2}} = \frac{1}{\sqrt{5}+\sqrt{2}} \times \frac{\sqrt{5}-\sqrt{2}}{\sqrt{5}-\sqrt{2}} = \frac{\sqrt{5}-\sqrt{2}}{5-2} = \frac{\sqrt{5}-\sqrt{2}}{3}$ ب) $\frac{2}{\sqrt{5}+\sqrt{3}} = \frac{2}{\sqrt{5}+\sqrt{3}} \times \frac{\sqrt{5}-\sqrt{3}}{\sqrt{5}-\sqrt{3}} = \frac{2(\sqrt{5}-\sqrt{3})}{5-3} = \frac{2(\sqrt{5}-\sqrt{3})}{2} = \sqrt{5}-\sqrt{3}$ ج) $\frac{8}{4+\sqrt{2}} = \frac{8}{4+\sqrt{2}} \times \frac{4-\sqrt{2}}{4-\sqrt{2}} = \frac{8(4-\sqrt{2})}{16-2} = \frac{8(4-\sqrt{2})}{14}$ د) $\frac{1}{\sqrt{x}-\sqrt{y}} = \frac{1}{\sqrt{x}-\sqrt{y}} \times \frac{\sqrt{x}+\sqrt{y}}{\sqrt{x}+\sqrt{y}} = \frac{\sqrt{x}+\sqrt{y}}{x-y}$